We are making a major effort to develop the utility of mass spectrometry to assist in the definition of integral membrane proteins and (especially ion channels) at atomic resolutions using diffraction - methods. Currently, the structure effort consists of three components: (a) work on high-level expression and purification of ion channels, (b) development of methods for growing two dimensional crystals (for electron microscopy studies) using small quantities of channel protein and (c) X-ray crystallographic studies of ion channel domains and soluble regulatory proteins that bind to ion channels. Our goal is to obtain high-resolution structures of the full, integral membrane ion channel through X-ray crystallography. By combining the exquisitely detailed functional information obtainable using patchrecording methods with three-dimensional structural data from X-ray crystallography, the central questions concerning the mechanisms of ion channel function can be answered. Mass spectrometry is beginning to have a major impact in facilitating this work - e.g., in elucidating compact domains of the ion channels.